The state’s largest public-employee union may kill Gov. Cuomo’s much-touted plan for an office to prosecute or discipline workers abusing people with mental disabilities who are under state care — unless they get an absurd giveback, The Post has learned.

The Civil Service Employees Association, in private negotiations with Cuomo’s office last week, linked approval of disciplinary penalties to be taken against workers found guilty of abuse to the unrelated granting of bonuses to state workers who agree to withdraw from the state’s costly health-insurance plan.

Under a labor pact negotiated with the CSEA last year, the Cuomo administration agreed to pay bonuses of between $1,000 and $3,000 to state workers who opt out of the state health-insurance plan for a plan provided by their spouses.

But a source close to the administration said the CSEA now insists that the bonuses be granted to state workers who are married to each other, under the incorrect idea that one spouse can drop out while the other stays in, thereby covering them both and saving the state money.

Under such an arrangement, there would be no state savings because the cost of insuring both state workers would remain the same, the source said.

It would affect about 1,700 employees and could wind up costing the state up to $6 million, the source said.

“This is insane. How f–king arrogant is that, they have the chutzpah to think the state would agree to that?’’ the source said.

CSEA has publicly claimed to support Cuomo’s proposed new Justice Center, which would have prosecutors and trained investigators to pursue complaints of patient mistreatment, abuse and neglect.

But the source said the union’s demand could kill it.

“The state will never agree’’ to that, the source concluded.

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Many influential Democrats have all but written off their Senate colleagues’ hopes of recapturing the majority in the Legislature’s upper house in the wake of this month’s unanimous Court of Appeals decision upholding the GOP plan to create a 63rd Senate seat.

The seat, part of a controversial redistricting plan approved by Cuomo this year, was a classic gerrymander, with boundary lines drafted to favor a GOP candidate, wealthy Assemblyman George Amedore, of Rotterdam, near Schenectady.

Meanwhile, incessantly self-promoting political “reformer’’ Bill Samuels, son of one-time gubernatorial hopeful Howard “Howie the Horse” Samuels, issued an embarrassing attack on the Court of Appeals decision, saying, “Legal it may be, but reform it is not.’’

Samuels, a wealthy Democrat with a seemingly desperate need for publicity, apparently didn’t realize the state’s highest court is supposed to interpret the law, not “reform’’ its political system.

“Bill’s father was such a brilliant guy that it’s a shame to see what’s happened to the son,’’ was how the Democratic insider put it.